Method and apparatus for testing metals



OR RE 1a.aa9BEST A AILABL C/OPYN 888mb R00" J. A. SAMS El AL July 4,1933. Re. 18,889

METHOD AND APPARATUS FOR TESTING METALS 3/ I Original Filed Feb. 5. 19252 Sheets-S eat 1 F113. 2. FLB. 3.

Inventors James A. Same VLI'QLL F. Shaw a M 1, 4%

Their Attornqy m O O R In C r a B S J. A. SAMS ET AL July 4, 1933.

METHOD AND APPARATUS FOR TESTING METALS 2 Sheets-Sheet 2 Original FiledFeb. 5, 1925 SAMPLE NUMBER Inventors James A. Burns VLrSLL F. 5hc1wTheir Attorney Reissuecl July 4, 1933 UNITED STATES PATENT OFFICE JAMESA.. SAMS, OF SCHENECTADY, AND VIRGIL F. SHAW, OF S'l'ZCl'lI'liA NEWYORK, ASSIG-NORS TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORKMETHOD AND APPARATUS FOR TESTING METALS Original No. 1,789,196, datedJanuary 13, 1931, Serial No. 7,107, filed February 5, 1925. Applicationfor reissue filed December 23, 1931.

Our invention relates to a method and apparatus for testing magneticbodies such for example as steel cutting tools to determine theirservice-ability.

Steels are generally tested With a view to determining their suitabilityfor some specific purpose; for example, the suitability of a steelcutting tool for continuous service depends upon such properties as itsresistance to wear and shock, its elasticity and brittleness, its grainstructure, the eil'ect of heat treatment and its chemical composition.These properties are largely interdependent and it is therefore possibleto approximately predict the serviccability ot' a particular piece ofsteel for a given purpose by the determination of the characteristics ofsome one of its properties such as the magnetic property.

Steel has been tested by determining its chemical composition. Such testrequires appreciable time, destroys the part tested and does not takeinto consideration the condition of the material due to heat treatment.Steel has also been tested by the scleroscope, an instrument fordropping a hardened point upon the specimen and noting the rebound, andby the Brinell method, which is carried out by measuring the depth ordiameter of an impression made in the material under test by a test ballunder pressure. Such tests are also more or less destructive and areonly indicative of surface conditions.

\Ve have discovered that the reaction of steel to magnetism is alsoindicative of its properties and that this reaction when properlyapplied and controlled, may be used to determine the service-ability ofsuch material to a high degree of accuracy and our invention relates toa method of and apparatus for the practicable application of thisprinciple to the testing of magnetic materials.

In carrying our invention into effect, we subject the material undertest to sudden or cyclic changes in magnetic flux such as an alternatingmagnetic field and obtain a comparative measurement of the so-callediron losses which occur in the material when thus magnetized.

The features of our invention which are Serial No. 582,887.

believed to be novel and patentable will be pointed out in the claimsappended hereto. lfor a better understanding of our invention, referenceis made in the following description to the accompanying drawings inwhich Figs. 1, 2 and 1' are schematic representations of different testunits developed in accordance with our invention, Fig. l is a wiringdiagram showing how the apparatus maybe conlu-cted tortcstingpl-irposes. 5 to 8 inclusive are hysteresis loops taken from ourmagnetic tester under dili'crent conditions. Fig. 9 shows by means ofcurves a. comparison of the test results obtained by our method andother methods and Fig. 10 represents a portable test outfit embodyingouranvcntion as actually constructed.

'1 he apparatus which We have found best suited for carrying out ourinvention consists in general of a sensitive wattinctcr and a. magnetictest unit which we have chosen to call the duroscope and which comprisesa magnetic structure having a magnetizing coil and a potential coilarranged so that the piece of material to be tested may be magnetized bythis magnet and the resulting effect of the magnetization determined.The magnetizing coil and potential coil are respectively connected so asto iniiuencc the current and potential coils of the wattmeter and thecomparative readings of the wattmctcr, With and without the test piecein place, may be taken as an indication of the our lity ofserviccability ot' the test piece.

A suitable source of alternating current supply is preferable forproducing an alternating flux field. although a direct current sourcewith means for interrupting or revcrsing its circuit may also beemployed. Various regulating and calibrating deviccs are desirable. Inpractice, it has sometimes been found advantageous to compensate the\vattmcter and duroscopc circuits so that the wattmetcr reads zero whenthe test piece is omitted from the duroscopc. place the duroscope on thetest piece so that the latter is magnetized thereby, adjust the circuitsto bring the wattmeter deflection back to Zero and use the position ofthe circuit adjusting means as an indication for the serviceability ofthe test piece. This may be called the null method of test in analogy tothe generally known null method of galvanometer tests. To those who arefamiliar with the use of the galvanometer as used in the testinglaboratory, it will be evident. that there are various ways of carryingout the test as thus outlined. Consequently, we do not wish to limit ourinvention to the particular apparatus or procedure hereinafterspecifically described.

Figs. 1 to 3 illustrate different test units or duroscopes which willfirst be described. Fig. 1 shows a cone shaped soft iron shell 10 whichinstead of coming to a point at its small end, terminates in acylindrical portion 11. Through the axis of this cone shaped shell is asoft iron core piece 12. Around the core piece in the main portion ofthe cone is wound a magnetizing coil 13 and around the core in the smallcylindrical portion 11 is wound a potential coil 14. The magneticcircuit between the core.and shell at the large end of the cone isclosed by a soft iron member 15. The magnetic circuit at the smallcylindrical end of the device is arranged to concentrate the flux to asmall area and is adapted to be closed by the piece of material to betested when the test unitis placed on a flat surface of such material.

- The device is preferably arranged to be adjustably supported above thematerial to be tested by a bail 16 and a spring 17. The device may bemade of any convenient size but generally need not be greater than 3inches in maximum diameter.

It will be apparent that there will be some transformer action betweenthe magnetizing and potential coils when the former is energized with analternating current, which transformer action will be eatly increasedwhen a test piece of magnetic material forms an armature across theconcentric pole pieces adjacent the potential coil. It will also beapparent that the nature and magnitude of this transformer action in thelatter case will vary with the magnetic nature of the test piece. Thesedifferences will show up when the magnetizing and potential coils arerespectively connected to influence the current and potential coils of awattmeter.

In Fig. 2 we have shown a tester in a cylindrical form having amagnetizing coil 13 and two potential coils 14: and 14a at oppositeends, all wound around the central core 12, in the cylindrical shell 18.This tester is adapted for comparing a standard sample which is placedover one end with an unknown sample which is placed over the other end.The two potential coils may be connected to oppose each other and inseries with the potential coil of the wattmeter.

The test units of Figs. 1 and 2 are adapted for testing pieces havingfiat surfaces.

In Fig. 3 we have shown a test unit for testing pieces having irregularsurfaces. In this unit, we have the central core piece 12 about which iswound the magnetizing coil 13 and the potential coil 14. The shell 19about the magnetizing coil is cylindrical except that portion about thepotential coil which is cone shaped, as represented at '10. The upperend of the magnetic circuit is closed by a magnetic bridge member 21 andthe lower end of the circuit is substantially closed by the cone shapedmember 20. A holder and terminal block 22 is provided. \Vith this testunit it will appear that the transformer action will be increased whenthe rounded point of the extension 2:3 of the central core member isplaced on a magnetiz able object.

In Fig. 4 we have represented a wiring diagram together with circuitadjusting means suitable for use with our magnetic tester. In thisfigure, 24 represents a source of alternating current supply. In thisinstance we have represented a rotary converter with resistance means 25for adjusting the direct current supply so as to vary the fro quency ofthe alternating currentend. The direct current circuit of the rotaryconverter includes the control switch 26 shown open. The current coil 27of the wattnieter and the magnetizing coil 13 of the magnetic test unitare connected in series through an adjusting resistance 28, an ammeter29, and a control switch 30 to the alternating current end of the rotaryconverter. The potential coil 31 of the wattmeter is connected in serieswith the potential coil 14 of the magnetic test unit, which unit isrepresented as that shown in Fig. 1. A multiple double throw switch 32is provided which is used in connection with 'an adjustable transformer33 when the. null method of test is employed. When the switch 32 isthrown up, the potential circuit between the wattmeter and the test unitis closed through the connection 34.

In testing a piece of material with the circuits thus arranged, thefrequency generated by the rotary converter is first adjusted to thevalue for which the apparatus has been calibrated by means of therheostat- 25. The switch 30 is closed and the rheosi at 28 adjusteduntil the ammeter 29 shows a current value for which the apparatus hasbeen calibrated. A wattmeter reading is then taken. There being no testpiece adjacent the potential coil 14, the wattmcter reading will be acertain amount which will be the same whenever these same conditions ofthe test circuit are reproduced. The material to be tested is placedacross the concentric pole pieces of the tester adj accnt the potentialcoil 14. When this occurs. the transformer action is increased and therealso occurs a shifting of the phase angle between the magnetizing andpotential currents. This shifting of phase is due to the so-called ironlosses in the material being tested. It is known for example that hardsteel has a considerable hysteresis loss. A certain amount of eddycurrent flux loss is also included. This change in condition results ina new deflection of the Wattmeter. The magnitude of the watt-meterdeflection will vary with the hardness of the steel tested and may thusbe calibrated with various samples of known hardness and thereafter usedto indicate the hardness of unknown test pieces. The flux penetrates toan appreciable extent into the body of the test piece so that theindication is not merely of the surface hardness of the material, butalso for an appreciable distance beneath the surface. The testpiece mayof course be moved along adjacent the test coil and tests made every fewinches with considerable rapidity, the. variations of the wattmeterindication, if any, indicating the difierent degrees of hardness. v

In some cases the null method of test is desirable, in which case theswitch 32 of Fig. 4 is thrown down. The frequency and cur rent isadjusted to that for which the apparatus is calibrated as before.Current is also supplied from the rotary converter to the primarywinding 35 of the adjustable inductance device or transformer 33 throughthe switch contacts 36 and adjusting resistance 55. The secondarywinding of this inductance device is made up of two coils 37 and 38connected in series with the potential circuit through switch contacts39.

The core 42 of the transformer varies in cross-section, the primaryWinding 35 being wound about the largest section. The secondary coil 38is stationary and is wound about the smallest section of the core. Thegreater are of the core between coils 38 and 35 gradually increases incross-section and the coil 37 is movable about this portion of the coreby means of an arm 40 to which the coil 37 is suitably secured. Whencoil 37 is close to coil 35 on the larger part of the core, thetransformer action is a maximum and gradually diminshes as the movablecoil is moved about the gradually diminishing section of the core. Thepotential thus induced in coils 37 and 38 is opposed to that induced bythe magnetizing coil 13 in the potential coil 14. and by varying thecurrent in coil 35 and the position of coil 37. the wattmeter readingmay be brought to zero both before and after the magnetic test piece isin place. The arm 40 carries a pointer cooperating with a scale 41 whichis suitably calibrated in terms of hardness or durability. In practice,the pointer is set at a zero reference point of the scale and thecurrent in coil 35 adjusted to bring the wattmeter deflection to zerowith no test piece adjacent the potential coil 14. Then the test pieceis placed in testing position and the secondary coil 37 is adjusteduntil a zero reading of the wattmeter is again obtained.

The hardness is then indicated by the position of pointer 40 in scale41. The null method has the advantage that variations in the voltage andfrequency of the alternating current supply aifect both the compensatingcircuit and the main test circuit alike so that errors due to suchvariations are eliminated.

In order that a better understanding may be had of the invention.reference is made to Figs. 5 to 8 inclusive. These figures representhysteresis loops obtained from our testing unit shown in Fig. 2 underdifferent conditions and taken by a cathode ray oscillograph. The.sensitivity of the apparatus was greatly diminished for these tests.

Fig. 5 represents the hysteresis loop with no test specimen adjacent thepotential coils and shows that the circuit is compensated to obtain azero wattmeter deflection. Fig. (i represents a hysteresis loop with thesame adjustment of the circuit as in Fig. 5,but with a hard steel testpiece in testing position at one end only.

Fig. 7 represents a similar loop for a normal steel test piece and Fig.8- for a soft steel test piece. These loops show that the permeabilityof the soft steel is greater than that of the harder steel but that fora given flux density, the hysteresis loss of the harder steel isgreater. The soft steel due to the greater permeability has the higherlosses for the excitation used and will give the greater wattmeterdeflection. From this it will be observed that instead of an ordinarywattmeter we could use a cathode ray oscillograph. The wattmeter howeveris sufficiently sensitive and is much less cumbersome to use.

During the calibration of our apparatus, a number of steel samples ofdifferent degrees of hardness were carefully prepared. These samplesconsisted of high speed steel pieces which were quenched at 1300 C. anddrawn at various temperatures to vary their hardness. They were testedby the Brinell, scleroscope and the method invented by applicants withthe following results:

ifiliif. a Sample No. de Brinell a 0 cams grees scope dumsm e C. drawnp 1. 100 642 95. 68 243. 2. 200 637 100. 261i. 5 3. 300 622 96. 87 272.4. 400 612 97. 87 278 5. 425 H14 100.37 272. 5 Ii. 450 595 97. 62 270 7.475 608 99. 25 272 B. 500 591 93. 25 273 9. 525 615 98. 285 10. 550 62298. 56 297 II 575 635 99. T5 312. 5 l2 600 631 100. 0 3'27 13. 625 60898. 50 325 I4. 650 601 99.43 322 l.' 700 590 94. 62 360 I6 750 400 78.B7 385 The comparative results of these tests are shown plotted in Fig.9 and illustrate the greater uniformity and accuracy of appli- BESTAVAILABLE COPY cant-s method of test. At a drawing tem perature of about(500 C. occurs what is known in the steel industry as the critical pointand where a decided change in the physical structure of the steel takesplace. \Vith the Brinell and sclcroscope methods of test, particularlyunsatisfactory results are invariably obtained at this point probablydue to the fact that these tests are essentially surface tests.

lVe have also determined by experiments that variations in the strain ofsteel may be detected by our apparatus. For example, we have found thata given steel sample will give a certain 'attmeter deflection when inthe unstrained condition, but that if the piece is compressed, thewattmeter deflection will increase appreciably and that the increaseddeflection is proportional to the compression strain and that the testcan be reproduced with fairly uniform results. It is believed that thisfeature will prove to be. of considerable value in testing steelstructures under strainto determine their factor of safety.

The apparatus which we have described may be put up in portable form soas to be carried about and the test carried out wherever electric energyis available. In places where electric energy is not available asuitable storage battery may be included in the apparatus. One suchportable set as actually constructed is shown in Fig. 10 where therelative size of the various parts may be seen. The control resistances25. 28 and 55 and the annneter 29 are contained in the cover of acarrying case 44 shown open. Compartments are also provided in the coverfor the three types of testunits 1. 2 and i which cor respond to thetest units shown in Figs. 1, and 3 respectively. A number of standardsamples of steel are shown at 45. An adjustable support for the testunit 1 is shown at 46. The portable wattmeter 47 shown resting on thetop of the case may also be housed in the cover of the case. Theadjustable transformer is housed in the base portion of the case withthe arm 40 and scale 41 exposed when the case is open. The handle shownat 48 is that of a reversing switch for the transformer potentialcircuit and the handles for the control switches 26. 3'2 and 39 areindicated by corresponding reference numerals. The rotary converter 2 Lis provided with a carrying handle like those of the case so that theentire apparatus may be carried about by one person. The various circuitconnections between the interior and exterior of the case are preferablycarried through detachable plug switches. not shown. in the r at wall ofthe case.

In accordance with the provisions of the patent statutes. we havedescribed the principle of operation of our invention, together with theapparatus which we now consider to represent the best embodiment thereofbut we desire to have it understood that the apparatus shown anddescribed is only illustrative and that the invention an be carried outby other means.

What we claim as new and desire to secure b liettcrs- Patent ot theUnited States. is:

1. Apparatus for determining physical properties of magnclizablematerials comrising a magnetic tester, having magne tizing and secondarycoils, an electrical measuring instrument having current and potentialcoils connected in series with said magnetizing and secondary coilsrespectively, a potential transformer. a common source of alternatingcurrent for energizing the said transformer and said magnetizing coil,means for connecting the secondary winding of said transformer in seriesopposition with the secondary coil of said magnetic tester, means foradjusting the secondary voltage of said potential trai'ist'ormer andindicating means associated with said adjusting means graduated toindicate. a physical property 'lu'ai.-tcristic oi the material to betested.

A magnetic testing device comprising a magnetic core member, amagnetizing coil wound about the body of said core, a potential coilwound about said core adjacent one end, and a. magnetic shellconcentrically enclosing said coils. said shell being reduced adjacentlhc potential coil for coi'icentrating the flux of the device to a smallarea thereat. the potential coil end of said device being designed to beplaced against the object to be tested substantially as and for thepurpose set forth.

3. magnetic testing device comprising a magnetic core member, amagnetizing coil wound about the body portion of said core member. apotential coil wound about said core member adjacent one end, a magneticshell concentrically enclosing said coils, the shell being reducedadjacentthe potential coil end to concentrate the flux of the device toa small :11 a. thcreat, and a magnetic member connecting said core andshell at the opposite end, the core atthe potential end of the devicebeing extended beyond the shell and shaped to make suljistantially ajoint contact with the mat rial to be tested.

at. A magnetic testing device comprising a magnetic core member. amagnetizing coil wound about the body of said eore,a potential coilwound about said core adjacent one end, and a magnetic shell consistingof a cone shaped portion surrounding said magnetizing coil and acylindrical portion surroundin said potential coil, the potential coilend of said device being designed to be placed against the object to betested substantially as and for the. purpose set forth.

5. A magnetic testing device comprising a magnetic core member, amagnetizing coil wound about the body portion of said core member, apotential coil Wound about said e. APPLNS core member adjacent one end.a magnetic shell consi. ting of a cone-shaped po .tion surrounding saidmagnetizing coil and a c \'lin drical portion surroimdinc' saidpotential coil. the Vlll1l'llllill portion of said shell. being: aontinuation of the small end of the cone-shaped portion. and a magneticmember connm'tine said core and shell at the large end of thecone-shaped portion ot said shell. the eyliiulrical end of said devicebeing designed to be placed against the object to be testedsubstantially as and for the purpose set. forth.

ti. The method of te ting a magnetizable bodv which includessimnltaneouslv establishing a magnetic tlnx in. a standard of knownmagnetism affecting: properties and in said bod respectively by means ofa magnetic force and producing tor inspection a representation of theinstantaneous value. variations of a cycle unit of the current pr ducedby a i'lift'erence in said maauetic tlunes due to a difference in amagnetism atl'eetine' property of said standard and said odv.

T. The method of testing a HIEIQ'HUt'iZH lQ body which includessinuiltaneonslv establishing a magnetic finx in a standard of knownmagnetism a tt'e tine' properties and in said bod} reapect-ivelv bymeans of a ma netic force, and producing a continuous reprei entation ofinstantaneous value variations in successive cycle? of the differentialcur rent produced hv a difference in eaid magnetic tluxes due to adifference in a magnetism affecting property of staid atandard and saidbody.

8. The method of teetine' a magnetizable. body which includessinulltaneously e tablishing: a magnetic. flux in a standard of knownmagnetism affecting properties and in said body respectively by means ofa magnetic force, effecting relative movement between said standard andsaid body and pro- BEST AVAILABLE Co during for inspection arepresentation of successive inatantaneous value Variations of thecurrent produced by a difference in said magnetic lluxcs due to adi'tlerenee in a mag:- netism affecting property of said standard andditt'erent portions of .said body.

9. The method of testing a magnetizable body which includes producing awave form image of the current induced in the secondary ot' atransformer with said standard positioned in the etfective fieldthereof. produein a wave form image of the current induced in thesecondary of said transformer with said magnetizable body positioned inthe l ective field thereof, and comparing said wave form images.

l The method .of testing which includes subjecting a specimen to amagnetizing force in a transformer. proi'lncing' a representation of therelationship between instantaneous values of current induced in thesecondary circuit of the transformer while the specimen is in theefiiective magnetic field thereof. subjectimg the specimen to inspectiont r determination of its physical and/or chemical properties.two-relating said representation with the results of said inspection.subjecting another specimen in a transformer to a magnetizing forcehaving the same value and characteristics as those of the magnetizingforce to which the first specimen was subjected. and coi'nparing therepresentation at the relationship between instantaneous values ofcurrent induced in the secondary circuit of the transformer while thesecond specimen is in the effective field thereof with said firstmentioned repreeentzLtimLsktO determine the likeness or unlike- Hess ofsaid specimens.

in witness whereof. we have hereunto set our hands.

JAMES A. SAMS. VIRGIL F. SHAW.

